Commercial electric power generators provide electric power which is subsequently transformed into a high voltage/lower current power for transmission for substantial distances over conventional power distribution lines. The output from the generator is generally routed through a terminal box in which a relatively large copper core carries the output current to the step-up transformer which increases the voltage and lowers the current for low loss transmission. Although the cables leaving the generator through the terminal box are quite large (as much as a six inch diameter solid copper cable) and their resistance is low, due to the extremely high current levels carried by the cable, a substantial amount of heat is generated.
In the past, generators have been cooled by hydrogen gas and this gas was passed through the bushings (where the conductor passes through the terminal box) to cool the bushing. At conventional commercial power generation levels, this was sufficient to prevent temperature extremes in the terminal box. However, with the advent of extremely high power generation systems, it has been necessary to obtain even greater heat transfer in the area of bushings which has been achieved by going to water cooled bushings. While water cooled bushings serve to maintain the temperature of the bushing at a relatively low level, due to the extremely high current levels and varying magnetic fields generated by those currents, proximity heating (eddy current heating) of the floor and walls of the terminal box result in undesirable temperatures in the terminal box, The water cooling of the bushings is not sufficient to remove sufficient heat so as to keep the floor and walls of the terminal box at appropriate temperatures.